Abstract
Anthropogenic carbon dioxide (CO2) emissions from cities have significantly increased over the past several decades along with rapid urbanization. To what extent anthropogenic CO2 emissions generated from cities can be offset through conserving or increasing carbon (C) stored within urban areas themselves is a significant scientific question. The role of urban street trees in offsetting anthropogenic CO2 emissions still remains uncertain. Here, using data from field surveys, tree growth measurements and governmental statistical yearbooks, we estimated the C storage and C sequestration capacity of street trees in Beijing. Results showed that the C density and C sequestration rate in Beijing’s urban street trees were about 1/3 ~1/2 of the corresponding magnitudes of non-urban forests in China. However, the total C sequestration of street trees in Beijing’s urban districts was 3.1±1.8 Gg C yr-1 (1 Gg = 109 g) in 2014, equivalent to only about 0.2% of its annual CO2-equivalent emissions from total energy consumption, indicating a rather limited role in offsetting overall anthropogenic CO2 emissions.
Highlights
More than half of the world’s population lives in urban areas, and this figure will continue to increase at a rate of 4% a decade by 2050 (UN, 2015)
The comparison suggests that C storage and sequestration per unit for urban trees in Beijing is at a higher level relative to other cities (Table 4), which might relate to the fact that in Beijing, the street tree planting protocol usually sets tree interval from 3 to 5 m which makes tree density in Beijing higher
It should be realized that the C sequestration of street trees becomes insignificant when compared with the total anthropogenic CO2 emissions and should not be considered as an effective mechanism to offset CO2 emissions in Beijing
Summary
More than half of the world’s population lives in urban areas, and this figure will continue to increase at a rate of 4% a decade by 2050 (UN, 2015). In this study we used field surveys, combined with tree growth measurement data and government statistics, to quantify the C storage and C sequestration rate of urban street trees in Beijing’s urban districts. The vegetation carbon storage of street trees in Beijing urban districts is 77.1 ± 4.1 Gg C with a sequestration rate of 3.1 ± 1.8 Gg C yr−1.
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